1. Field of the Invention
This invention relates to improved glass insulation for electrical wire and to a process for producing the same. In particular, the invention relates to glass insulation suitable for use in electromagnetic coil wire used in the close vicinity of liquid metal cooled nuclear reactors, especially to lift and hold reactor safety rods.
A controllable electromagnet is one of the best means of maintaining safety and versatility in the operation of lifting and holding the safety rods on the top of a nuclear reactor core. The coil windings of the electromagnet must be flexible enough to wind into a suitable coil, must be fully insulated to eliminate turn-to-turn or turn-to-ground short circuit failures, and must be capable of exerting enough force to lift and hold the rod assembly even at elevated temperatures. To obtain this force, the coil must have sufficient turns of wire in the coil capable of providing a large current. The turns should be in close contact to reduce losses. For application to a liquid metal cooled reactor the insulation must withstand temperatures at 600.degree. C. continuously, with possible temperature excursions as high as 750.degree. C. Additionally, the coil should be a strong monolithic structure capable of withstanding electrical and vibrational forces as well as radiation doses of at least 10.sup.7 rads.
2. Description of the Prior Art
Many different materials are commonly used to coat or cover electrical wire for the purpose of providing electrical insulation. Insulation presently known to be prior art is generally unsuited for use in an environment of high temperature and high radiation and also in an application requiring the wire to be formed into sharply bending turns. Insulation sufficiently flexible to form tight bends in the electromagnet generally does not perform well during long term exposure to high temperatures and radiation. Insulation appropriate to high temperature and radiation is generally not suited to tight bending of the wire, since such blends may induce cracks, flaking or other defects in the insulation, causing electrical shorts.
Consequently, it is desired to provide insulation for electrical wire which insulation generally does not flake off, crack or otherwise fail when the wire is formed and utilized in tight bends such as those occurring in the windings of an electromagnet and which insulation has good long-term properties in both high temperature and radiation environments.